Process for fractionating gaseous mixtures



H. J. Nucl-ICLs` JR., ET AL PROCESS FOR FRACTIONATING GASEOUS' MIX'IURES` Filed March 9, 19:54

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Patented May so, 1939 STATES v2.1601163 Paocnss Fon FRACTIONATING cuissons MIXTURE llenry Janney Nichols, Jr., Scotch Plains, and George L. Mateer, Roselle, N. J., assignors to Standard Oil Development Company, a corporation oi Delaware Application March 9, 1934, Serial No. 714,792

' 2 claims. (ci. aso-sse) '15 equipment.

In the drawing, numeral l denotes an absorber of the usual type receiving gas from line 2. This line may be supplied with a gas from a cracking coil still or other source. A typical composition 2.0 for such a gas is 50% methane, 20% C2 hydrocarbons, C3 hydrocarbons,vl0% C4 hydrocarbons, andthe remainder C5 and higher. The absorber preferably contains plates which are alternately joined to the opposite sides so that the ascending gases and a descending absorbent oil may come into intimate contact. Other types of absorbers may be used such as packed towers. Absorbent oil is supplied to the upper part oi the absorber` I through line 3. An outlet 6 is provided to remove the'gas after contacting with the absorbent oil. The absorbent oil is removed from the absorber I by line 5 and by means of .pump 6 is passed into the upper part of absorber "I. Line 8 is provided to pass avgas such as that '35 obtained by stabilization of cracked distillate andA containing hydrocarbon vapors having low numbers of carbon atoms. A typical composition for such a gas is 5% methane, 20% C2 hydrocarbons, 50% C3 hydrocarbons, and 25% C4 hydrocarbons. Fresh oil may be introduced into the absorber through line 9. The gas, after contacting with p the absorbent oil, is removed through line I0. The absorbent oil containing the hydrocarbon vapors that have been absorbed is removed through line II and by means of pump I2 is vpassed. into the upper part of absorber I3. Line I4 is used to supply gas to the lower part of this tower.- The gas that is supplied to this tower is cracked gas resulting from the cracking stills and refinery gas obtained during the'dlstillation of crude oils, and low boiling fractions such as gasoline and kerosene. A typical composition for such. a gas mixture is 30% methane, 20% Cz 55 hydrocarbons, 20% Ca hydrocarbons, 15% C4 hydrocarbons, and the remainder C5 and higher hydrocarbons. Fresh oil is supplied to the absorber I3 through line I5.

The resulting gas, after contacting with the absorbent oil, is removed through line -I6. The 5 absorbent oil containing the absorbed gases is then passed through line II'bymeans of pump I8 and valves I9 and 20 into still 2l where the absorbed vapors are vaporized and passed through line 23 to condenser, not shown. The absorbento oil from which all the desired hydrocarbon vapors have been removed is then passed through line 25 and may be returned to the absorbers tobe recycled once more.

To illustrate this process the following example isgi-venzln connection with the manufacture of hydrogen it is desirable to scrub a gas substantially free of propane as well as all higher. hydrocarbons. At the same time it is desirable to discard butaue to fuel in order to meet v ola- 20 tility specifications on motor gasoline. In addition to these two conditions it is desirable to produce a gas free of'butane and high in propane cut and therefore propylene for the manufacture of isopropyl alcohol. i 25 Cracking coil gas is passed into' absorber l where sumcient fresh lean oil is delivered through line 3 to substantially remove all the hydrocarbons having three or more carbon atoms.- 'I'he gas released from absorber I through line 4 is 30 used in connection with the manufacture of hydrogen. Stabilizer gas, containing perhaps 25- 35% butane, is delivered through line 8 to absorber l. The absorbent oil from absorber I is delivered through line 5 and pump 6 to anin- 35 termediate point in absorber 1. The necessary amount of' stripped lean oil is pumped to the top of absorber 'I through line`9' to complete the removal of all butane. 'I'he gas released from absorber 'I throughline I0 is used in connection with 40 the manufacture of isopropyl alcohol. The major portion of theI renery gas, in which the partial pressure of butane is less than in the absorbent oil from the absorber 1, is delivered through line I4 to the absorber I3. 'I'he absorbent oil from absorber? is delivered through line II and pump I2 to an intermediate point in absorber I3. Thus, relatively large quantities of this undesirable butane will be flashed .off into gas from the absorbent oil and released from the top of absorber I3 through .line I6 to the fuel system. The necessary amount of stripped lean oil is pumped to the top of absorber I3 through line I5 to insure the complete recovery of' all -55 the pentane and heavier hydrocarbons. The absorbent oil from the absorber I3 containing only a small fraction of hydrocarbons having less than four carbon atoms and a major fraction of hydrocarbons having more than four carbon atoms is then removed to still 2l through line I1 and pump I8; In these stills` all desirable hydrocarbons are lvaporized and condensed and used for blending with gasoline. The stripped oilu from the stills is then recycled through the process.

i It is highly essential in this process that deflnite ratios of absorbent oil and gas that is contacted with it be maintained in order that the desired fractions of hydrocarbon vapors may be` removed and the desired fractions .oi' hydrocarbon vapors may be separated. By this process, with a minimum oil circulation a hydrocarbon vapor is obtained which consists substantially of methane ethylene and ethane. Another fraction is obtained which consists substantially of propane, propylene and small portions of ethane,`

ethylene and methane, and is used in the manufacture of alcohol. The third separated hydrocarbon fraction that is not absorbed by the absorbent oil and which consists substantially of .butane and small portions of propane, propyiene,

'I'he foregoing description is merely illustrative and various changes and alternative arrangements may be made within the scope of the appended claims in which it is our intention to claim all inherent novelty in the invention as broadly as the prior art permits.-

We claim:

1. A process for recovering from renery gases of different compositions, mainly composed of C1 to C4 hydrocarbons, a gas mixture adapted for conversion by steam into hydrogen and a gas mixture composed mainly of Ca hydrocarbons adapted for use in the manufacture of isopropyl alcohol, which comprises contacting a gas mixture relatively richer in C1 and C2 hydrocarbons than in C: and C4 hydrocarbons with a sufElcient amount of absorbent oil having solvent properties for all of the constituents to absorb hydrocarbons having more than 2 carbon atoms, whereby a residual gas composed mainly of C1 and Cz hydrocarbons is obtained and the absorbent oil is enriched in Ca and C4 hydrocarbons, and contacting the thus enriched oil with a gas mixture in which C3 hydrocarbons predominate, and containing C4 hydrocarbons, whereby, through the effect of vapor pressure, the C: hydrocarbons in the absorbent y oil and in the gas mixture are given off and 'th oil becomes enriched in C4 hydrocarbons.

2. A process according to claim l, in whic the absorbent oil rich in C4 hydrocarbons is contacted with a gas mixture containing C5 and higher hydrocarbons together with C1 to C4 hydrocarbons and having a lower partial pressure of C4 hydrocarbons than the absorbent oil, whereby C4 and lower hydrocarbons are flashed oif and the Ct and'higher hydrocarbons are retained in the absorbent oil.

HENRY JANNEY NICHOLS, JR.

GEORGE L. MATEER. 

